A new medical pump-reservoir implanted inside the belly might keep thousands of people with liver cancers alive for years by continually bathing their livers with an anti-cancer drug.

The same kind of implantable pump, easily refilled with a hypodermic needle, is also being tried in brain, head and neck cancers.

Here, too, early results are called promising. With this system, only the cancerous organ, and not the whole body, need be subjected to the powerful chemotherapy that ordinarily severely limits the cancer-fighting dose.

The liver can be subjected to doses 100 to 400 times greater than otherwise possible. "The patients feel better and they often go back to work," Dr. William Ensminger of the University of Michigan Medical Center in Ann Arbor, site of the new advance, reported yesterday.

University doctors told how they have implanted the new system to infuse a drug called FUDR (for fluorodeoxyuridine) in 61 people with liver cancer, a tumor that often takes its toll in a few months.

Almost all had colorectal (colon and/or rectal) cancers that had spread to their livers, which kills about half such patients.

The Michigan treatment is given in the university's Clinical Research Center, one of nearly 100 started by the Division of Research Resources of the National Institutes of Health to hasten the application of medical knowledge to patients.

Of 47 "evaluable" patients -- those whose course was not affected by other events -- 40 are still alive, and the cancers have regressed or shrunk in more than eight cases in 10. Of the six patients treated the longest -- 24 to 28 months -- four are alive.

"Without this treatment," Ensminger said, "two of these four would have been dead within two to three months. The other two would probably have been dead within six to eight months.

"This is still no cure. But we are talking about one of the most quickly fatal cancers. There is no doubt in our minds but that this is the most effective way to treat it."

Though the stubborn cancers are still there, he said, in many cases they have stabilized and are not growing. "With better drugs and combination of methods, including the pump, I believe that within five years we'll be talking about real cures in at least a small percentage of cases," he said.

Shaped like a hockey puck and not far from the same size -- 3.6 x 1.2 inches -- the implantable pump was developed at the University of Minnesota for other purposes.

Doctors at several centers have tried externally carried reservoirs and pumps to infuse cancers continually. They have improved results in some cases, but the internally implanted pump with a catheter positioned very precisely in the hepatic (liver) artery does even better, Ensminger said.